This application claims the benefit of Korean Patent Applications No. 2001-5043 filed on Feb. 2, 2001, which is hereby incorporated by reference as if fully set forth herein.
1. Field of the Invention
The present invention relates to a method for performing Chemical Vapor Deposition (CVD), and more particularly to Atomic Layer Deposition (AID) Processes.
2. Discussion of the Related Art
In the field of thin film technology requirements for thinner deposition layers, better uniformity over increasingly larger area substrates, larger production yields, and higher productivity have been driving forces behind emerging technologies developed by equipment manufactures for coating substrates in the manufacturing of various semiconductor devices.
Electric devices are recently highly integrated to have smaller size and light weight because of semiconductor devices. Specifically, the manufacture of Ultra Large Scale Integration is possible due to the improved thin film deposition technologies manufacturing the semiconductor devices.
Namely, process control and uniform film deposition achieved in the production of a microprocessor can be achieved. These same factors in combination with new materials also dictate higher packing densities for memories that are available on a single chip or device. As these devices become smaller, the need for greater uniformity and process control regarding layer thickness rises dramatically.
Various technologies well known in the art exist for applying thin films to substrates or other substrates in manufacturing steps for integrated circuits (ICs). Among the more established technologies available for applying thin films, Chemical Vapor Deposition (CVD) is an often-used and commercialized process. Atomic Layer Deposition (ALD), a variant of CVD, is a relatively new technology now emerging as a potentially superior method for achieving uniformity, excellent step coverage, and transparency to substrate size. ALD, however, exhibits a generally lower deposition rate than CVD.
CVD is flux-dependent application requiring specific and uniform substrate temperature and precursors (chemical species) to be in a state of uniformity in the process chamber in order to produce a desired layer of uniform thickness on a substrate surface. These requirements becomes more critical as substrate size increases, creating a need for more complexity in chamber design and gas flow technique to maintain adequate uniformity.
In the CVD method alluded above, deposition rates of thin films and characteristics of deposited thin films depend on circumstances of the process chamber, such as chamber temperature and pressure, accompanying precursor""s flow rate. Another problem in CVD coating, wherein reactants and the products of reaction coexist in a close proximity to the deposition surface, is the probability of inclusion of reaction products and other contaminants in each deposited layer. Also reactant utilization efficiency is low in CVD, and is adversely affected by decreasing chamber pressure. Still further, highly reactive precursor molecules contribute to homogeneous gas phase reactions that can produce unwanted particles which are detrimental to film quality. Therefore, Low Pressure Chemical Vapor Deposition (LPCVD) by which step coverage and uniform thickness of thin film are improved is now in the spotlight in forming thin films on a substrate surface. However, when using LPCVD, the deposition rates decrease, thereby attempting to introduce reaction gases having higher partial pressures. This also causes the problems that gas reactions occur in an undesired position of reaction chamber, so the possibility of contaminants in the deposited layer increases.
On account of above-mentioned problems, Atomic Layer Deposition (ALD) has been researched and developed. Although a slower process than CVD and although the similarity to CVD in using precursor reactions, ALD demonstrates a remarkable ability to maintain ultra-uniform thin deposition layers over complex topology. This is at least partially because ALD is not flux dependent as described earlier with regards to CVD. This flux-independent nature of ALD allows processing at lower temperatures than with conventional CVD rocesses.
ALD processes proceed by chemisorption at the deposition surface of the substrate. The technology of ALD is based on concepts of Atomic Layer Epitaxy (ALE) developed in the late 1970s or early 1980s, for example, U.S. Pat. No. 4,058,430, for growing of polycrystalline and amorphous films of ZnS and dielectric oxides for electroluminescent display devices. The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD appropriate reactive precursors are alternately pulsed into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas purge. Each precursor injection provides a new atomic layer additive to previous deposited layers to form a uniform layer of solid film. The cycle is repeated to form the desired film thickness.
A good reference work in the field of Atomic Layer Epitaxy, which provides a discussion of the underlying concepts incorporated in ALD, is Chapter 14, written by Tuomo Suntola, of the Handbook of Crystal Growth, Vol. 3, edited by D. T. J. Hurle, .COPYRGT. 1994 by Elsevier Science B. V. The Chapter title is xe2x80x9cAtomic Layer Epitaxyxe2x80x9d. This reference is incorporated herein by reference as background information.
To further illustrate the general concepts of ALD, an ALD process for forming a film of materials A and B, as elemental materials, will be explained hereinafter. A solid layer of element A is formed over the initial substrate surface, and then a first purge is processed to form a single atomic layer of element A. Over the A layer, a layer of element B is applied, and then, a second purge is performed. Therefore, the layers are provided on the substrate surface by alternatively pulsing a first precursor gas A and a second precursor gas B into the region of the surface, resulting in providing the AB solid material.
Meanwhile, gaseous reactants and their bonding energy are dependant on a substrate and a material which are under the deposited thin films. When forming a single-crystalline layer on a surface of single-crystalline silicon substrate, there are a lot of active portions which are distributed uniformly on that silicon substrate surface and on which gaseous reactants are deposited. By way of applying a thermal energy to the gaseous reactants with maintaining the substrate at a high temperature, gaseous reactants are uniformly deposited and decomposed in the surface of substrate, and thus, silicon atoms are rearranged and grow to a single-crystalline thin film in accordance with the single-crystalline surface of the substrate. At this time, the physically deposited gaseous reactants exist on the chemically deposited silicon layer provided on the substrate surface, and thus such gaseous reactants act as impurities and contaminants that decrease purity of deposited layer. Therefore, a purge process proceeds after such a depositing process. Namely, the substrate heated with the aid of a suitable heating source is subjected to the gaseous reactants, and then purged using an inert gas. Therefore, the chemically deposited reactants are left on the substrate, whereas the physically deposited reactants are removed from the substrate, resulting in forming a single atomic silicon layer on the single-crystalline silicon substrate.
This type of procedure is also disclosed in U.S. Pat. No. 4,389,973, for example. According to that patent, the wafer is sequentially subjected to a plurality of gaseous reactants in order to form thin films thereon. During the deposition processes, the gas phase diffusion barrier is used as a carrier gas in order to prevent reactions between source gases, or the carrier gas is used to remove the residual gases after injecting each source gas.
U.S. Pat. No. 4,767,494, as another example, discloses the compound semiconductor thin film formed by growing a plurality of molecular layers one over another. According to that invention, while a carrier gas and a small quantity of hydride containing an element in Group V or VI are normally flowed, an organometallic compound which is diluted with hydrogen and which contains an element in Group V or VI and a hydride which is diluted with hydrogen and which contains an element in Group V or VI are alternately introduced over a substrate so that an atomic layer of an element in Group III or II and an atomic layer of an element in Group V or VI are alternately grown over the substrate. Therefore, grown layers having a high degree of purity can be obtained.
In U.S. Pat. No. 5,130,269, the method of growing a gallium arsenide single crystal layer on a silicon substrate comprises steps of growing a buffer layer of aluminum arsenide on the silicon substrate by Atomic Layer Epitaxy (ALE), and growing the gallium arsenide single crystal layer on the buffer layer epitaxially.
As known from the above-mentioned patented invention, ALD has been developed to overcome the drawback of CVD, so that ALD in resent obtains better uniformity over increasingly large area substrates and excellent step coverage. Contrary to CVD where gaseous reactants simultaneously flow into a reaction chamber to deposit thin films on a substrate, ALD alternately subjects the substrate to gaseous reactants, and includes an inert gas purge process to remove residual gases, thereby dropping the impurity content in the deposited layers. For example, when forming a thin film on a substrate using two vapor phase reactants, one cycle of the gas sequence for the growth of the thin film includes four sub-steps. In a first sub-step, a first vapor phase reactant is introduced into a reaction chamber in which a substrate is positioned. Thereafter, residual gas is removed from the reaction chamber, i.e., a second sub-step. In a third sub-step, a second vapor phase reactant is introduced into the reaction chamber to form a thin film with the first layer formed of the vapor phase reactant. In a four sub-step, residual gas is removed again from the reaction chamber. This conventional ALD technology is disclosed in U.S. Pat. Nos. 4,413,022 and 6,015,590. As a method for removing the residual gas, the inert gases are used in U.S. Pat. No. 4,413,022, and the vacuum pump is adopted according to U.S. Pat. No. 6,015,590.
FIG. 1 is a graph illustrating one cycle of forming a thin film using a conventional ALD technology. In FIG. 1, one cycle T of forming a thin film includes a first quantity t1 representing the time during the first sub-step, a second quantity t2 representing the time during the second sub-step, a third quantity t3 representing the time during the third sub-step, and a fourth quantity t4 representing the time during the fourth sub-step. The time quantities t2 and t4 over which the residual gases are removed are longer than the time quantities t1 and t3 over which the substrate is objected to the gaseous reactants. As a result, the process of forming a thin film needs a sufficiently long time, and manufacturing yield of thin film is reduced.
At this point, a lot of methods and plans are introduced to reduce the time required in each sub-step. However, the time quantities t1 and t3 should maintains for a sufficient time because these should be enough to distribute and absorb the injected gaseous reactants over the whole surface of the substrate. Furthermore, it is difficult to reduce the time quantities t2 and t4.
For example of applying the above-mentioned ALD method, a process of forming an alumina (Al2O3) film using the conventional ALD is presented in Applied Physics Lettersxe2x80x94Volume 71, No. 25, pp. 3604-3606, Dec. 22, 1997. At a deposition temperature of about 370 degrees centigrade (xc2x0 C.), tri-methyl-aluminum [Al(CH3)3, TMA] is introduced into the reaction chamber during the first sub-step t1 of about one second under the pressure of about 230 mTorr. Then, the introduction of TMA is stopped, and Ar gas is introduced into the reaction chamber during the second sub-step t2 of about 14 seconds. The above-mentioned Ar gas prevents the TMA from being over-adsorbed on the silicon substrate, and discharges a residual non-reacting gas out of the reaction chamber. Thereafter, a de-ionized water (DIW) vapor is introduced into the reaction chamber during the third sub-step t3 of about 1 second under the pressure of about 200 mTorr. Subsequently, the introduction of TMA is stopped, and Ar gas is introduced again into the reaction chamber during the fourth sub-step t4 of about 14 seconds such that another residual non-reacting gas is discharged out of the reaction chamber.
After one cycle, specifically 30 seconds, during the above-mentioned process, the obtained film is less than 0.3 nm in thickness. Therefore, for the fabrication of 10 nm film, the above-mentioned cycle should be repeated for about 33 times. In other words, it takes more than 990 seconds to fabricate the 10 nm film by applying the ALD. Accordingly, although the use of the conventional ALD method can produce a thin film having a low-impurity content, it takes longer processing time while depositing the film on the substrate.
Meanwhile, if a substrate or a underlayer is polycrystalline or amorphous, the energy level of active portion varies depending on substrate""s or underlayer""s crystal structure and surface state because the active portions on which the gaseous reactants are deposited exist in a various state. Therefore, when the gaseous reactants are objected to the substrate or underlayer, the active portion""s position and the binding energy are determined by the gaseous reactant type. At this point, as mentioned before, the physically deposited reactants are cleaned from the reaction chamber in accordance with the quantity of injected inert gas and the chamber pressure or the vacuum pump capacity. However, at the time of that cleaning process, the chemically deposited reactants can be exhausted from the substrate or underlayer if the binding energy is weak in the active portion. Therefore, the layer thickness, which is obtained during one cycle, is various depending on the process condition although the gaseous reactant is the same. To obtain a determined thickness, thus, the deposition process alluded before should be repeated a lot more times. This results in increasing depositing time and decreasing manufacturing yield.
As mentioned before, in the CVD method, a lot of gaseous reactants are injected into the reaction chamber and converted into radicals, thereby forming thin films by interactions of radicals. At this time of forming the thin films, by-products are produced and then trapped into the deposited layers due to the continuous apply of gaseous reactants.
However, in case of the ALD method, after introducing the gaseous reactants to the substrate, the purge process is repeatedly performed over each reactant introduction. Therefore, the impurity concentration in the deposited layer and the layer thickness over one cycle are determined in accordance with the quantity of inert gas and the time consumption. Furthermore, the hourly productivity is varied by these inert gas quantity and the time passage. In other words, when the inert gas quantity increases and when it takes longer processing time to purge the active portion and to pump down the reaction chamber for the purpose of decreasing the impurity ratio from the layer, the adhered reactants are rapidly reduced due to the removal of deposited elements. These cause the decrease of layer thickness less than single atomic layer and produce the inferior production, thereby deteriorating the hourly productivity. Moreover, due to the injecting and purge processes, there are other problems of shifting gas injection devices, and thus, the time delay is unfortunately caused, and productivity is further declined. To overcome these problems, the complex facilities having various equipments and devices are recommended, but those facilities increases the production cost in the field of semiconductor devices.
Accordingly, the present invention is directed to a method of forming a thin film that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of forming a thin film, which presents an excellent step coverage, a uniform layer composition and a high degree of purity in the thin film.
Another object of the present invention is to provide a method of forming a thin film, which has a short processing time of layer deposition.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to achieve the above object, the preferred embodiment of the present invention provides a method of forming a thin film in a first chamber where a heater and a suscepter are located. The method includes the steps of disposing an object on the susceptor so as to form the thin film thereon; heating the object; a first sub-step of introducing a first gaseous reactant into the first chamber such that the first gaseous reactant is absorbed on the object to form an absorption layer; a second sub-step of introducing a second gaseous reactant into the first chamber such that the second gaseous reactant reacts with the absorption layer absorbed on the object; and a third sub-step of introducing a reducing gas into the first camber such that the reducing gas reduces by-products and impurities of the first and second gaseous reactants.
In one aspect, the first, second and third sub-steps are sequentially repeated as one cycle so as to form the thin film having an ultra-high degree of purity. A thickness of the thin film having the ultra-high degree of purity is 0.3 nm after performing the first and second sub-steps one time. The thin film having the ultra-high degree of purity is 10 nm in thickness after final deposition process.
In another aspect, three-time repetitions of the first and second sub-steps and one time of the third sub-step form one cycle of deposition and several repetitions of one cycle form the thin film having a high degree of purity. A thickness of the thin film having the high degree of purity is 1 nm after three-time repetitions of the first and second sub-steps. A thickness of the thin film having the high degree of purity ranges from 0.2 to 0.3 nm after one time of the first and second sub-step. The thin film having the high degree of purity is 10 nm in thickness after final deposition process.
In another aspect, more than ten-time repetitions of the first and second sub-steps and one-time of the third sub-step form one cycle of deposition and several repetitions of one cycle form one of crystalline and amorphous thin films. A thickness of each of crystalline and amorphous thin films ranges from 2 to 3 nm after one cycle of deposition. Each of crystalline and amorphous thin films is 10 nm in thickness after final deposition process. A thickness of each of crystalline and amorphous thin films ranges from 0.2 to 0.3 nm after performing the first and second sub-steps one time.
In the above-mentioned method, the first and second sub-steps form an oxidized layer and the reducing gas is one of oxygen and ozone. The first and second sub-steps form a nitride layer and the reducing gas is one of ammonia and hydrazine.
The above-mentioned method further includes the step of thermal-treating the object in a second chamber after the third sub-step when the deposited thin film is used as a dielectric layer for the electric device. The second chamber is a vacuum chamber and the reducing gas of the third sub-step is introduced in the second chamber. The reducing gas introduced in the second chamber is excited into a plasma during the thermal treatment for the dielectric layer. The dielectric layer is one of alumina thin film and tantalum pentoxide (Ta2O5) thin film. The method further includes the step of forming a polycrystalline silicon layer on each of alumina thin film and tantalum pentoxide (Ta2O5) thin film. Forming one of alumina thin film and tantalum pentoxide (Ta2O5) thin film and forming the polycrystalline silicon layer are sequentially performed in the first and second chamber.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.